As DRAMs increase in memory cell density, there is a continuing challenge to maintain sufficiently high storage capacitance despite the continuing goal to further decrease cell area. One principal way of increasing cell capacitance is through cell structure techniques. Such techniques include three-dimensional cell capacitors, such as trenched or stacked capacitors. Yet as feature size continues to become smaller and smaller, development of improved materials for cell dielectrics as well as the cell structure are important. The feature size of 256 Mb DRAMs is on the order of 0.25 micron, and conventional dielectrics such as SiO.sub.2 and Si.sub.3 N.sub.4 might not be suitable because of small dielectric constants.
Chemical vapor deposited oxide films, such as, for example tantalum oxide (Ta.sub.2 O.sub.5), BaTiO.sub.3 and SrTiO.sub.3 films are considered to be very promising cell dielectric layers. For instance, the dielectric constant of Ta.sub.2 O.sub.5 is approximately three times that of Si.sub.3 N.sub.4. Capacitor constructions have been proposed and fabricated to include the use of one or more of the oxide materials as a capacitor dielectric layer. However, diffusion relative to the oxide materials can be problematic in the resultant capacitor constructions. For example, tantalum from Ta.sub.2 O.sub.5 tends to undesirably out-diffuse from dielectric layers comprising tantalum oxide. Further, materials from the adjacent conductive capacitor plates can diffuse into the tantalum-comprising dielectric layers. In either event, the dielectric properties of the dielectric layer are adversely affected in a less than predictable or an uncontrollable manner.
A method of inhibiting diffusion between tantalum oxide and adjacent materials is to surround the tantalum oxide with a material that constitutes a diffusion barrier layer. Suitable materials for utilization as diffusion barrier layers are materials comprising transition metals (such as, for example, ruthenium, osmium, rhodium, iridium and cobalt), and can include transition metal oxides (such as, for example, ruthenium oxide, osmium oxide, rhodium oxide, iridium oxide and cobalt oxide). The transition metals are typically deposited by chemical vapor deposition (CVD) utilizing metal-comprising precursor compounds. The metal-comprising precursor compounds generally comprise a transition metal coordinated with one or more Lewis base ligands in the form of a complex. Exemplary metal-comprising precursors are (cyclopentadienyl)Rh(CO).sub.2, and (1,3-cyclohexadiene)Ru(CO).sub.3. During a CVD process, the metal-comprising precursors are provided in a reaction chamber with a substrate and subjected to temperature and pressure conditions (and, in some instances, to a plasma or photolysis) to decompose the precursor and cause release of metal from the precursor. The released metal is then deposited on the substrate. A difficulty in utilizing the above-describe metal-comprising precursors in CVD processes is that the precursors frequently decompose prematurely. Such decomposition can occur while the precursors are stored outside the chamber and can result in formation of dimers or molecular clusters of the transition metal precursors. The resulting materials comprising dimers or molecular clusters are generally less volatile than are the original metal-comprising precursors, and accordingly can be difficult to utilize in CVD processes. It would be desirable to develop methods for CVD of metal-comprising precursors which avoid the above-described difficulties.